Stabilization of the dimensions of felt materials



United States Patent "ice 3,092,888 STABILIZATION OF THE DIMENSIONS OF FELT MATERIALS Louis R. Mizell, Bethesda, Md., and Julian Berch, Washington, D.C., assiguors to Western Felt Works, Chlca 0 ll]. NE l )rawing. Filed Jan. 12, 1959, Ser. No. 786,038

8 Claims. (Cl. 26-18.5)

This invention relates .to a method for stabilizing the width of felt materials against relaxation shrinkage which consists in overstretching the material while wet, i.e., stretching it a width far beyond the desired finished width of the material, which finished width is much greater than the normal relaxed width of the material, preferably after first treating the material with a chemical reducing agent, and after such overstretching permitting it to relax a width near such desired finished width. Preferably such method of width stabilization also includes steaming the felt while in its overstretched condition and/ or during or preliminary to the stretching thereof.

The invention also relates to a method for stabilizing the thickness of felt materials which consists in simultaneously heating and over-c ompressing the material while wetted by an initial content of at least 20% by weight of liquid, also preferably after first treating it with a chemical reducing agent.

The term felt material as used herein is intended to designate a fabric which is built up by the interlocking of fibers induced by a combination of mechanical working, chemical action and heat, without spinning, weaving or knitting. :Felt materials to which our method is applicable must contain at least 20% wool or an equivalent feltable animal fiber such as Karak-ul, mohair, alpaca, cattle hair and the like. The remaining fiber constituent may be animal fiber, vegetable fiber (e.g. cotton), synthetic cellulosic fiber (e.g. viscose) or synthetic thermoplastic fiber (eg. nylon, Dacron).

The mechanical Work performed in forming the felt may be carried out by one or more operations known as hardening, fulling, squeezing, rolling, pounding, oscillating, vibrating or needling. Felts thus formed are known in the art as wool felt, pressed felt, mechanical roll felt, mechanical sheet felt, apparel felt, tailoring felt, pad felt, backcheck felt and other designations for felt materials formed by a felting process involving hardening or fulling. Our method is also applicable to needled or punched felts as long as they contain at least 20% wool or other animal protein-type fibers.

The relaxation shrinkage of felt in the widthwise direction has long been a serious problem and is the primary obstacle to Wider acceptance of this material in the apparel industry and because of this problem dry cleaners are reluctant to Work on apparel made from felt. The main complaint of users regarding felt garments has been the excessive shrinkage of such garments. in tests conducted with apparel manufactured from conventional felts it was found that a typical dry cleaning caused felt fabrics to shrink 3 to 5% in the widthwise direction. Steaming on the buck of a press was found to cause shn'nkages of from 6 to 15% in width. Thus felt garments which have been processed in the conventional manner cannot be steam pressed due to the danger of excessive relaxation shrinkage. Tests on conventional apparel felts have further shown that a wet cleaning (handbrushing with lukewarm water and a neutral detergent) produced average relaxation shrinkage of 20.5% in the widthwise direction. When liquid is spilled on a womans skirt made from unstabilized felt the skirt puckers badly and becomes useless.

'By relaxation shrinkage is meant that shrinkage which occurs in all textile materials or products which have shrinkage processes such as the Sanforizing process and 3,092,888 Patented June 11, 1963 not been stabilized by special processing. Certain strains are put into the textile materials by the processing machinery during manufacture of the material. Relaxation shrinkage is the relieving of such strains. Such shrinkage occurs in the finished, unstabilized textile material when the product is exposed to a humid atmosphere, when it is wetted with water, when steam pressed, when dry cleaned in a detergent system, and often during normal mechanical agitation such as during normal wearing of a textile garment.

The relaxation shrinkage of apparel and other lightweight felts in the lengthwise direction is not a serious problem. Though the methods to be described herein and embodying the present invention are not specifically designed for stabilizing felt in the lengthwise direction since as stated above shrinkage in this direction is not a serious problem, yet we have found that when our process is used the felt will be at its desired and relaxed length during the final drying operation and if care is exercised in performing the finishing operations, it.will be stabilized at said length as well as at its desired finished width.

Where felts are being used for industrial purposes, variations in thickness after the felt has been finished become a significant problem. When such felts are cut into thin walled pieces such as washers, seals, gaskets and the like or allowed to stand for long periods of time in a humid atmosphere the thickness of the felt increases considerably. This is a serious disadvantage in many cases since industrial felts are generally sold according to a specified thickness which includes an allowable thickness range. -If, after being finished, the thickness changes so as to exceed this permissible range then the material may Well be rejected by the buyer. Furthermore, if use of the felt requires that it be cut into small pieces such cutting will cause an appreciable increase in the thickness of the felt and this will often render the material'useless as when the small felt pieces were intended to fit into spaces of fixed dimensions. A further limitation is that since conventional felts increase in thickness and distort in shape when wetted they cannot be used where water is present or ,where water is likely to be formed by condensation.

It can be seen that stabilization of the width of felt materials is of prime importance when such felts are to be used for apparel purposes. Relaxation shrinkage in the widthwise direction may also be a serious problem where felts are used for filtering purposes as well as in various other well known applications of lightweight felt. It can further be seen that stabilization of the thickness of felt materials is of prime importance where thick felts are being used for industrial purposes. In both of these situations felt is sold under specifications which contain a narrow range of allowable thickness, width, length and density. Conventional felts can be made to conform temporarily to such specifications but they do not remain within such specifications when put in storage or when used.

It should be understood that while stabilization of width is of especial importance when lightweight felt is being used for apparel purposes, filtering or in various other well known applications for such felt and stabilization of thickness is of especial importance when thick felt is being used for industrial purposes, yet many situations can arise where it is necessary to stabilize a felt material against both width wise relaxation shrinkage and against variations in thickness.

There are many processes known to the art for the stabilization of woven fabrics which involve pre-shrinking of the fabric. Thus woven cotton fabrics are usually .stabalized against relaxation shrinkage by compressive the Rigmel process. Woven wool fabrics are generally pre-sln'unk by a London shrinking process. When these processes are used the fabrics must be made wider and commercially set by applications of steam and boiling .water.

A further process for setting wool fabrics is decribed in the Dalton et al. Patent 2,669,002 which deseribes a method of treating a fabric with an aqueous alkaline solution of pH 9 to 12 and subjecting the wet fabric to high intensity infra-red radiation. Many published articles describe other methods involving the use of alkali and heat to set wool materials.

All of these known commercial, patented or published processes for setting wool fabrics have as their objectives either: (1) to pre-shrink or pre-relax the dimensions of the fabrics, i.e., set the material in the relaxed or nearly relaxed dimensions; (2) to remove irregular and hidden strains from the fabric which adversely affect dyeing and other processes; or (3) to uniformly pre-shrink the fabrics so as to prevent the formation of cockles, creases and other forms of uneven shrinkage at later stages of manufacture. Such processes which involve pre-shrinking of the fabric are such that the fabric is set at its normal relaxed dimensions and they are entirely unsatisfactory in the stabilization of felt for several important reasons:

First, it is not practical to pre-shrink felt material and still finish and sell it at a width as large as 72inches, which is the standard width for apparel felts, and at a prescribed thickness and weight per unit area. In order to satisfactorily make non-woven felts of a specified weight, thickness and density it is necessary to shrink the batt of fibers in width to a width before drying of about 50 to 60 inches and the felts have to be finished at a width of at least 72 inches. By conventional processes this is accomplished by stretching the felts on the dryer to 72-78 inches such'that drying at this width temporarily sets the felt dimensions after the final finishing operations (shearing, pressing, folding, etc.) at the specified width of 7 2-7 3 inches. To pre-shrink felts by presently known methods would cause them to be finished at a width of 50 to 60 inehes i.e. the normal relaxed width. Thus to apply such pre-shrinking processes to stabilize felt materials would require that said materials have a normal relaxed width of about 72 inches as compared to the conventional relaxed width of 50 to 60 inches. It can be seen that such methods would require extremely wide and expensive carding, hardening and other machines not now available to the industry and would require unusually thin fiber batts. The process embodying the present invention avoids this problem since it is not a preshrinking process but rather a stabilizing process and the felt is set at a width considerably greater than the normal relaxed width.

Secondly, we experimented with all such previously known methods as could be applied to felt and found that they did not effect satisfactory stabilization of felt materials. We tested a number of resin treatments, woolreacting chemical treatments, and other wool-setting treatments including steaming and the process described in Dalton et al. We treated the felts with resins and alkalies under a wide range of conditions and dried them under various conditions on tenter frames with the felts at their normal or regular dried widths. Other felts were steamed while at their regular dried widths. The best of these treatments or operations only reduced the relaxation shrinkage of the finished felts by, for example, from a normal 20% widthwise shrinkage to a 15 to 18% widthwise shrinkage. Thus we found that none of these previously known processes were satisfactory for our purposes nnless eombined with our over-stretching technique lwhigh will be hereinafter described.

One of the objects of this invention is to provide a method of stabilizing the width of lightweight felt materials against relaxation shrinkage which method will render the felt materials suitable for use in apparel, for

filtering purposes and for the many other known uses for such lightweight felts without damaging any of the desirable, mechanical, chemical or functional properties of said material. I

Another object of this invention is to provide a method for stabilizing the thickness of heavy industrial felts such that said felts will not increase appreciably in thickness when wetted with water or when cut into thin walled pieces such as washers, seals and the like.

'A further objective of this invention is to provide a method for stabilizing the width of felt materials against relaxation shrinkages such that said felt can be made in the usual manner with equipment which, except for a tenter frame which is larger than those now in use, is entirely standard, and such that said felt is stabilized at a width which is much wider than the normal relaxed width of the material before drying.

A still further object of this invention is to provide a method of stabilizing the width of lightweight felt materials which will also improve the uniformity of the texture of said materials by reducing voids and the like.

Other objects and advantages of this invention will be apparent from the following description of a preferred embodiment thereof:

In order to stabilize the width of felt material by our process felts are preferably, although not in all cases necessarily, first treated, after dyeing (or if not dyed then after washing), with an aqueous solution containing 0.5l% by weight of a chemical reducing agent. Any chemical reducing agents which are known to reduce the disulfide linkages in animal fiber keratin may be used in this process. We have found, however, that reducing agents containing sulfur produce the best results and we have further found that reducing agents containing sulfur in which the valence of the sulfur is 6 or less are particularly satisfactory for use in our process. Some of the chemicals which were tested and found to produce highly satisfactory results are sodium bisulfite (or sodium meta bisulfite), thiogylcollic acid and its salts (e.g., ammonium thioglycolate), sodium sulfoxylate formaldehyde, sodium hydrosulfite, zinc hydrosulfite and sodium sulfitc. Reducing agents containing sulfur and their adducts with formaldehyde e.g. sodium sulfoxylate formaldehyde and various metal salts of reducing agents containing sufur e.g., sodium and zinc hydrosulfite will also produce satisfactory resutls. Some reducing agents other than those containing sulfur will produce satisfactory results, for example, compounds conatining boron i.e., metal and amine borohydrides such as sodium or potassium borohydride; certain reducing agents containing nitrogen i.e. derivatives of hydroxylamine such as hyroxyl ammonium sulfate. As speciiied above a 0.5-1% solution is generally satisfactory but the optimum concentration varies depending upon the style of felt being treated and the particular reducing agent being used and concentrations from 0.255% may be quite satisfactory in some cases. In this pre-: ferred embodiment sodium bisulfite is used because it is one of the least expensive chemicals, easy to handle, non-toxic, and does not require rigid control of treating conditions nor leave an unpleasant odor in the finished materials.

The chemical treatment may be carried out in either a regular washer with the felt in rope form or in a padder with the felt in open-width form. With the latter After the sodium bisulfite treatment the felt is extracted by the use of standard squeeze rolls or by other suitable means such that after extraction the felt will preferably contain solution approximately equal in weight to that of the felt itself. Thus if 100 pounds of felt were being treated then after treating and extraction the total weight of the treated felt should preferably be about 200 pounds. Extraction, however, is not a critical process and considerable variation is permissible.

The felt to be stabilized in width, having been chemically treated and extracted, is preferably then stretched in width approximately 55% beyond the width of the felt in its treated and relaxed state. This stretching process will hereinafter be referred to as overstretching. We have found that the chemical treatment above referred to effects considerable stabilization and that it is an improvement over the methods previously known. Wet have further found, however, that over-stretching is a highly important step in our stabilization process and satisfactory stabilization of the width of felt mate-. rials cannot ordinarily be achieved by a mere chemical treatment alone. We also found that with certain types of felt, such as those composed of 50% viscose in blends with wool, the chemical treatment was not necessary and that satisfactory stabilization could be achieved by overstretching alone.

In this preferred embodiment a standard type tenter frame is used to effect over-stretching except that it is constructed so as to be wider than the conventional models since the latter are not capable of stretching the felt beyond about 86 inches in width. To aid the initial stretching it is desirable to expose the felt to live steam for a short time i. e., about 5 to seconds, as the material is entering the tenter frame and before it is'in the fully-stretched position. If large quantities of felt materials are to be processed it is desirable to enclose the tenter frame Within a steam chamber so that simultaneous stretching and steaming of the felt will be facilitated. Of course the process of stretching felt to the width of 72-78 inches (the standard drying width for apparel felt) and then allowing it to dry is well-known in the art. Overstretching, however, is quite different from the normal stretching process because it involves .stretching the material to a width far beyond the desired finished width. For example, if the desired finished Width is 72 inches and the width of the felt after fulling, washing, dyeing and chemical treatment is 60 inches, then in the over-stretching process the felt would be stretched to awidth of about 93 inches. It would then be dried at a width such that it would relax back to a stabilized width of 72 to 73 inches. The stabilized Width is thus in excess of 10% greater than the initial unstretched width of the wet and relaxed material. Merely to stretch the material to a width of from 72 to 78 inches as in the conventional drying operation will not achieve stabilization.

Ordinarily the 55% widthwise stretch, previously referred to, is equivalent to stretching the material an amount equal to from 2 to 2% times the difference be tween the desired finished Width and the Width of the felt in its chemically treated state (or after the last wet processing operation) and the latter stretch designation .is a satisfactory rule to follow if the desired finished width differs appreciably from the standard of 72 inches. It is always necessary to stretch the material well beyond the desired finished width but the optimum amount of over-stretch depends upon the type of felt being processed, the amount of wool or the amount and type of synthetic fiber in the blend, and the degree of widthwise felting shrinkage the felt received during its manufacture. Thus the optimum amount of stretch may vary so as to be anywhere from 1 /2 to 3 times the difference between the desired finished width and the width of the material after the last wet processing step.

After the felts are in the fully-stretched position it is beneficial to expose them to steam for about one minute because such steaming aids in the stabilization process. Some felts, if they have been chemically treated, do not have to be steamed in the over-stretched position in order to achieve satisfactory stabilization but even with these felts it is always useful to steam them as they enter the tenter frame in order to facilitate the stretching process. When steaming in the over-stretched position is found useful, the time of such steaming can be varied considerably, except that steaming times of more than 30 minutes will impair the strength and other properties of wool materials and steaming times of less than 1 minute are of little value. In the usual case the felts would be moving continuously on the track of the tenter frame while being steamed and the steaming time could then be regulated by the length of the tenter frame machine, the position of the steam outlets, and the speed of travel of the tenter frame track.

After the felts leave the tenter frame and steam chamber they are immersed in a water rinse bowl which removes most of the sodium bisulfite, if a chemical treatment was necessary. This rinse bowl may also contain a chemical sizing agent (e.g. starches, resins, rubber latices, etc.) which is normally applied to felts, provided the chemical is compatible with the bisulfite solution which builds up slightly in the rinse bowl. Thus it is not necessary to rinse the bisulfite treated felts in a separate bowl of water prior to standard application of a sizing agent if the sizing agent is compatible with the bisulfite.

Following the process steps outlined above the felts are further processed or handled in the conventional manner, except that special care should be taken to minimize the tension or pull on the felt in the lengthwise direction during final finishing operations such as shearing, pressing or folding, so that excessive relaxation shrinkage will not be put into the lengthwise direction of the felt during such final finishing. It will be noted that the process above described involves substantially no contraction lengthwise of the felt material during the widthwise stretching so the length thereof remains substantially the same as in the initial relaxed state, and this condition should not be disturbed, in the finishing operations. 7

As previously noted it is not necessary to apply the sodium bisulfite treatment in order to stabilize all types and styles of felt. With many styles of felt this treatment aids considerably in the stabilization process while with others stabilization can be achieved merely by overstretching or by over-stretching and steaming.

It is to be understood that the process being described stabilizes the felt at its finished width which is consider- During over-stretching this material is stretched to a width of approximately 87 to inches depending upon the type of felt being processed and its relaxed width after the last wet processing operation. Assuming such relaxed width to be approximately 60 inches, the overstretch would thus be to a width between approximately 40% and approximately 70% greater than such relaxed width. However, as above pointed out, the amount of overstretch is subject to variation depending on the type of felt being processed and the minimum effective amount in some cases may therefore be somewhat lower, say on the order of 35%. After being over-stretched the felt will relax to a width of about 72 to 73 inches and it can then be finished at this standard width at which it will be effectively stabilized. This method has been found to be extremely useful in effecting such stabilization and tests have shown that a standard shrinkage of 22% in thewidthwise direction can be reduced to a relaxation shrinkage of about 1 to 3%. In other words when a finished fabric or garment which has been treated 7 by our process is wetted in water or steamed the resulting relaxation shrinkage will be from about 1 to 3%, and such wetting and steaming are known to be the most severe causes of relaxation shrinkage.

Stabilization of the thickness dimension may be accomplished by or include substantially the same chemical treatment. used in width stabilization where such treatment is found to be desirable. Thus when thick industrial felts are being produced, or in any other situation where the thickness'of the felt is significant, the firststep in the thickness stabilization process is to treat the material with a solution of sodium bisulfite or other suitable chemical reducing agent and extract the material between squeeze rolls exactly as previously described. After being chemically treated the wet felt is simultaneously heated and compressed in thickness. The felt may contain anywhere from 20 to 300% of solution by weight when the pressing operation is begun but an amount from 30 to 100% of the weight of the felt is preferable in most cases.

The application of pressure on the felts to reduce the thickness can be achieved in several diiferent ways. Thus pressure can be applied by use of a standard flat bed hydraulic press or the felts can be compressed between heated rolls. Many other means of applying a compressional force will be satisfactory and in fact stretching the felts in width will in some cases achieve this result. In the latter case, however, it is important to note that stretching is utilized to reduce and compress the felt in thickness and the amount of stretching required is not necessarily similar to that previously described for the over-stretching width stabilization technique and will ordinarily be considerably less than that used in overstretching. Successful thickness stabilizationwas achieved by using pressures which reduced the thickness of the felts after the last wet processing operation from to 85% but in most cases optimum results will be achieved with pressures that reduce thickness from 30 to 50%. When felts are compressed by the thickness stabilization process being described the percentage reduction in thickness is considerably greater than that which occurs in any conventional pressing operation previously known to r the art and, therefore, this step will herein be referred to as over-compression.

The felts are heated while they are being compressed and while several methods of applying heat would be satisfactory a standard, steam heated flat bed hydraulic press is used in this embodiment. Heated rolls may also be used and if over-compression is achieved by stretching the material then beat may be applied by use of a gas fired drier. Felts can be successfully stabilized in thickness by using temperatures from 150 to 350 degrees F. depending upon the thickness of the material, the amount of compression, the dwell time in the press, and Whether or not a reducing agent is used. We have found the optimum temperature range to be from 210 to 260 degrees F. and if low temperatures in the order of 150 degrees F. are used a long dwell time of approximately 30 minutes may be necessary. The optimum time of compression or dwell time depends upon other inter-related variables. Thus if heated rolls are used to compress the felt the. time of compression may be less than 1 minute if thickness is reduced at least 50% and if a temperature over 300 degrees F. is maintained. If a flat bed press is used, then a compression time of 1 to 3 minutes would be satisfactory in conjunction with a reduction in thickness of '30 to 50% and a temperature somewhat less than 300 degrees F. If stretching is used to effect over-compression, then the dwell time would be the time of drying which is ordinarily about 30 to 60 minutes.

' We have found that the chemical treatment previously referred to will effect considerable thickness stabilization even where over-compression is not used. We have also found that with many types of felt the use of over-compression as above described will effect satisfactory thickness stabilization without use of a chemical reducing agent. We have further found, however, that in many cases satisfactory thickness stabilization can be achieved only by combining the chemical treatment and the overcompression.

It is quite important to note the distinction between merely reducing the felt thickness during conventional pressing of dry felts and our over-compression process. It is a well established mill procedure to include a pressing step in the final group of finishing operations. When felts are pressed in the conventional manner they are pressed while dry or while containing only a small amount of moisture, generally less than 20% by weight, whereas in our over-compression process the moisture content should be from 20% to by weight and while the upper limit may be exceeded in some cases the lower limit represents the minimum amount of moisture necessary for satisfactory thickness stabilization. Conventional dry pressing will reduce the felt in thickness so that it is in the desired thickness range but this finished felt thickness is only temporary and when the felt is later wetted in water, exposed to high humidity, or cut into narrow strips, it will return to the original thickness that it had prior to pressing. For example, a 0.600 inch felt, which was pressed dry in the conventional manner at 300 degrees F. for 3 minutes so as to be compr ssed to a finished thickness of 0.500 inch, increased in thickness to 0.584 inch when cut into strips 0.25 inch wide. The same felt increased to a thickness of 0.636 when wetted with water and dried. A felt of the same style stabilized by the thickness stabilization process described herein increased in thickness only 0.010 inch when out and when wetted and dried. That is a felt of the same style having an original thickness of 0.600 inch was treated.

with a 0.5% sodium bisulfite solution, extracted to a moisture content of 50% by weight, and over-compressed while wet so as to reduce its thickness to 0.33 inch. After over-compression it relaxed so as to have a finished, dried, stabilized thickness of 0.495 inch and when out and when wetted and dried it increased in thickness 0.010 inch to a final thickness of 0.505 inch.

After the simultaneous heating and pressing of the felt, it can be given any treatment, dried, and finished in the regular manner under the conditions used for the type of felt being processed.

This method can, of course, be applied in various ways and the present description should, therefore, be regarded as disclosing only an illustrative embodiment of the invention from which no unnecessary limitations should be implied.

We claim:

1. A method of stabilizing the thickness of felt material such that said material will not increase appreciably in thickness when wetted, exposed to a high humidity, or when out into small pieces, which consists'in wetting said material so that it contains more than 20% moisture by weight; over-compressing the said material while wet so as to reduce its thickness by an amount equal to from about 20% to about 85 of the thickness of the material in its wet and relaxed condition to' a reduced thickness which is substantially less than the desired finished thickness of said material; heating said material to a temperature between and 350 degrees B, said overcompression and said heating being performed simultaneously; and after a predetermined length of time releasing the compression and permitting said material to relax to its desired finished thickness.

2. A method of stabilizing the thickness of felt material such that said material will not increase appreciably in thickness when wetted, exposed to a high humidity,

or when out into small pieces, which consists in treating,

compressing the material While wet with at least approximately 20% by Weight of said solution so as to reduce its thickness by an amount equal to from about 20% to about 85% of the thickness of the material in its wet and relaxed condition to a reduced thickness which is substantially less than the desired finished thickness of said material; heating the material to a temperature between 150 and 350 degrees F., said over-compression and said heating being performed simultaneously; and after a predetermined length of time releasing the compression and permitting said material to relax to its desired finished thickness.

3. A method of stabilizing the thickness of felt material such that said material will not increase appreciably in thickness when wetted, exposed to a high humidity, or when cut into small pieces, which consists in treating said material with an aqueous solution containing 0.25 to by weight of a reducing agent containing sulfur in which the valence of the sulfur is less than 7; overcornpressing said material While wet with at least approximately 20% by weight of said solution so as to reduce its thicknes by an amount approximately 30%- 60% of the thickness of the material in its wet and relaxed condition to a reduced thickness which is substantially less than the desired finished thickness of said material; heating said material to a temperature of approximately 200-300 degrees F., said over-compression and said heating being performed simultaneously; and after a predetermined length of time releasing the compression and permitting said material to relax to its desired finished thickness.

4. A method of stabilizing against relaxation shrinkage the width of felt material at the desired finished Width and length dimensions, which consists in: 'overstretching said material while wet in a widthwise direction to an overstretched Width which is approximately 35% to 70% greater than the initial unstretched width of the wet and relaxed material and substantially exceeds the desired finished width, while maintaining the length of the material substantially unchanged; maintaining said material in such overstretched condition for a predetermined period of time; then reducing the tension on the overstretched material; and drying and thus relaxing such 10 material while it is still in a partially tensioned state to a stable finished width which is at least 10% greater than the initial width While the length thereof remains substantially the same as in the initial relaxed state.

5. The method of claim 4, with the additional step of applying steam to the material in at least one stage of the method.

6. The method of claim 4, with the preliminary step of treating said material with an aqueous solution including from about .25% to about 5% 'by weight of a reducing agent containing sulfur, the felt material in this case containing at least about 20% wool.

7. The method of claim 6, with the further step of extracting the treated material prior to the overstretching thereof to a liquid content of from about to about 120% of the weight of the untreated material.

8. A method of stabilizing the width of a felt material at a finished stabilized width of approximately 72 inches against relaxation shrinkage which consists in: wetting said material, thereby causing it to shrink to a normal relaxed width substantially less than said finished stabi lized Width; overstretching said material to a width of at least approximately inches; and after a predetermined length of time reducing the tension on said material and permitting it to dry and relax at substantially said desired finished width of approximately 72 inches.

References Cited in the file of this patent UNITED STATES PATENTS 8,444 Gambrill Oct. 21, 1851 1,008,249 Elsasser Nov. 7, 1911 1,688,088 Nakashian Oct. 16, 1928 2,253,102 Walker Aug. 19, 1941 2,338,386 Strake Jan. 4, 1944 2,646,341 Fetscher July 21, 1953 2,739,034 Fell Mar. 20, 1956 2,766,760 Bogaty et al. Oct. 16, 1956 2,983,569 Charle et al. May 9, 1961 FOREIGN PATENTS 563,638 Great Britain Aug. 23, 1944 626,336 Great Britain July 13, 1949 

1. A METHOD OF STABILIZING THE THICKNESS OF FELT MATERIAL SUCH THAT SAID MATERIAL WILL NOT INCREASE APPRECIABLY IN THICKNESS WHEN WETTED, EXPOSED TO A HIGH HUMIDITY, OR WHEN CUT INTO SMALL PIECES, WHICH CONSISTS IN WETTING SAID MATERIAL SO THAT IT CONTAINS MORE THAN 20% MOISTURE BY WEIGHT; OVER-COMPRESSING THE SAID MATERIAL WHILE WET SO AS TO REDUCE ITS THICKNESS BY AN AMOUNT EQUAL TO FROM ABOUT 20% TO ABOUT 85% OF THE THICKNESS OF THE MATERIAL IN ITS WET AND RELAXED CONDITION TO A REDUCED THICKNESS WHICH IS SUBSTANTIALLY LESS THAN THE DESIRED FINISHED THICKNESS OF SAID MATERIAL; HEATING SAID MATERIAL TO A TEMPERATURE BETWEEN 150 AND 350 DEGREES F., SAID OVERCOMPRESSION AND SAID HEATING BEING PERFORMED SIMULTANEOUSLY; AND AFTER A PREDETERMINED LENGTH OF TIME RELEASING THE COMPRESSION AND PERMITTING SAID MATERIAL TO RELAX TO ITS DESIRED FINISHED THICKNESS. 